Electroplating conductor roll

ABSTRACT

The purpose of the present invention is to provide an electroplating conductor roll with excellent high temperature abrasion resistance and corrosion resistance and excellent high temperature hardness. In an electroplating conductor roll, a composite carbide cermet-based thermally sprayed coating, which includes a composite carbide of WC and Cr3C2, and a ternary intermetallic compound binder metal of Cr, Ni and W, is formed on the surface of a metal roll. When the thermally sprayed coating is 100 mass %, the content of the composite carbide is 55-93 mass % and the content of the ternary intermetallic compound is 7-45 mass %. When the composite carbide is 100 mass %, the content of WC is 64-85 mass % and the content of Cr3C2 is 15-36 mass %.

TECHNICAL FIELD

The present invention relates to a conductor roll for electroplating.

BACKGROUND ART

In an electroplating line of cold-rolled steel sheets, a plating treatment is performed through a series of processes including an alkali washing process, a pickling process, a plating process, a washing process, and a chemical treatment process while conveying a cold-rolled steel sheet.

In the plating process, there is arranged a plurality of conductor rolls which energizes a cold-rolled steel sheet conveyed in a plating bath. Conductor rolls are required to be excellent in corrosion resistance, and also excellent in wear resistance and peeling resistance, and the like, so that their life is extended.

Patent Literature 1 discloses a conductor roll for electroplating with excellent corrosion resistance and wear resistance. The conductor roll is characterized in that a composite carbide cermet thermally-sprayed coating, which includes a composite carbide containing WC and Cr₃C₂ and one or two or more metals and alloys selected from Cr, a Cr—Co alloy, and a Cr—Ni alloy, is formed on the surface of a metal roll.

Patent Literature 2 discloses a conductor roll characterized in that a self-fluxing alloy thermally-sprayed layer containing a WC cermet is formed on the surface of a roll, and a WC cermet layer is further formed thereon. Patent Literature 2 also describes that the WC cermet layer preferably contains one or two or more selected from Ni, Cr, Ti, Nb, V, Cr₃C₂, and Ta in an amount of 50 to 80 mass % with respect to all components of the surface layer. As an example, a WC cermet layer containing 73WC-20Cr₃C₂-7Ni is disclosed.

CITATION LIST Patent Literature

Patent Literature 1: JPH10-110252

Patent Literature 2: JP2006-183107

SUMMARY OF INVENTION Technical Problem

Patent Literature 1 focuses on the use of a composite carbide including a combination of WC and Cr₃C₂, instead of a carbide including only one component, as a carbide constituting the main component of a cermet. That is, the corrosion resistance, which is insufficient with only WC, is compensated by combining Cr₃C₂ with WC, and the wear resistance, which is somewhat poor with only Cr₃C₂, is dealt with by combining WC with Cr₃C₂. Thus, an object is to combine WC and Cr₃C₂ to form a composite carbide, thereby to form a thermally-sprayed coating with excellent properties with respect to a plating solution.

The above-described Patent Literature 1 includes, as a binder particle, one or two or more metals or metal alloys selected from hard Cr, a Cr—Co alloy, and a Cr—Ni alloy. When these binder particles are thermally sprayed, a large amount of fine particles (fumes) including as a main component a Cr oxide is generated in a thermal spraying heat source at high temperature. It was found that this causes fumes to aggregate and deposit inside and on the thermally-sprayed coating, leading to the reduction in hardness of the thermally-sprayed coating, the falling-off due to wear, and the permeation of corrosive substances.

In Patent Literature 2, a cermet layer includes 73WC-20Cr₃C₂-7Ni, and does not contain a Cr oxide. However, the problem is that the corrosion resistance of Ni simple substance metal is not sufficient, and Ni is likely to corrode particularly in the corrosion environment of an oxidizing acid solution. Also, since Ni has poor wettability with WC and Cr₂C₃, a dense thermally-sprayed coating is difficult to obtain. This causes another problem in that the particle joint strength in the thermally-sprayed coating is low.

The present invention has been achieved in view of the above-described problems. An object of the present invention is to provide a conductor roll for electroplating which is excellent in high temperature wear resistance and corrosion resistance, and also excellent in high temperature hardness.

Solution to Problem

Examples of a carbide particle as a thermal spraying material may include WC, ZrC, TiC, and Cr₃C₂. The thermally-spraying with only these carbide particles results in the formation of a coating which is porous and low in adhesion. Therefore, these carbide particles are thermally sprayed onto a conductor roll for electroplating together with a predetermined binder metal to form a carbide cermet-based thermally-sprayed coating. In general, although WC is hard and excellent in wear resistance, a cermet-based thermally-sprayed coating formed with a combination of WC and a binder metal tends to be softer than a thermally-sprayed coating formed with only carbide particles. Furthermore, although WC is excellent in wear resistance, the corrosion resistance to a plating solution is weak with only WC. Accordingly, Cr₃C₂ needs to be used for the compensation.

That is, the present inventor compensates by Cr₃C₂ the corrosion resistance which is insufficient with only WC, while overcoming by WC the shortage of high temperature wear resistance due to the use of only Cr₃C₂. Also, the ternary intermetallic compound is used as a binder metal. Accordingly, the thermally-sprayed coating has not only high temperature wear resistance and corrosion resistance, but also high temperature hardness.

Herein, when the thermally-sprayed coating is 100 mass %, the composite carbide is preferably contained in an amount of 55 to 93 mass %, and the ternary intermetallic compound is preferably contained in an amount of 7 to 45 mass %.

Furthermore, when the composite carbide is 100 mass %, the WC is preferably contained in an amount of 64 to 85 mass %, and the Cr₃C₂ is preferably contained in an amount of 15 to 36 mass %

Advantageous Effects of Invention

According to the present invention, there can be provided a conductor roll for electroplating which is excellent in high temperature wear resistance and corrosion resistance, and also excellent in high temperature hardness.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a vertical continuous electroplating cell.

FIG. 2 is a front partial cross-sectional view of a conductor roll.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic view of a vertical continuous electroplating cell to which a conductor roll according to an embodiment of the present invention is applied. With reference to the drawing, plating tanks 11 are disposed in a multistage manner, and a plating solution M is stored in each of the plating tanks 11. It is noted that only one of the plating tanks 11 is illustrated in FIG. 1 for simplification of the drawing. The plating solution M may include any known plating solution such as a galvanizing solution and a tinning solution. A sink roll 12 is disposed to the plating tank 11. The conveyance direction of a metal strip S is changed from downward to upward by this sink roll 12. Also, a pair of electrode plates 13 is disposed upstream and downstream from the sink roll 12 in such a manner that a metal strip S is positioned between the pair of electrode plates 13.

A conductor roll 14 is disposed between the neighboring plating tanks 11. The conveyance direction of the metal strip S is changed from upward to downward by the conductor roll 14. Here, since the plating solution M adheres to the metal strip S exiting from the plating tank 11, the plating solution M adheres onto the roll surface of the conductor roll 14 when the metal strip S reaches the conductor roll 14.

A roll polisher 15 is disposed below each of the conductor rolls 14. The roll polisher 15 is driven between a contact position at which the roll polisher 15 is brought into contact with the conductor roll 14 and a spaced position at which the roll polisher 15 is spaced apart from the conductor roll 14. The movement of the roll polisher 15 to the contact position enables the roll polisher 15 to remove the plating solution M adhering to the conductor roll 14. At this time, the conductor roll 14 is subjected to sliding wear by coming in contact with the roll polisher 15. On the other hand, when the roll polisher 15 is in the spaced position, the conductor roll 14 is exposed to the corrosion environment due to the adhering plating solution M.

A positive electrode of an unillustrated DC power source is connected to the electrode plate 13, and a negative electrode thereof is connected to the conductor roll 14. These are applied with voltages to energize between the electrode plate 13 and the strip S. Thus, while the strip S passes through the plating tank 11, its surface can be continuously subjected to a plating treatment. However, the invention according to the present application can also be applied to a horizontal continuous electroplating cell in which the conductor roll 14 is constantly immersed in the plating solution M.

FIG. 2 is a front partial cross-sectional view of a conductor roll. A thermally-sprayed coating 12 b is formed on the surface of a roll body 12 a of the conductor roll 12. The thermally-sprayed coating 12 b is constituted by a composite carbide cermet-based thermally-sprayed coating which includes a composite carbide containing WC and Cr₃C₂ and a ternary intermetallic compound containing Cr, Ni, and W.

The present inventor can form a thermally-sprayed coating with excellent denseness, high temperature wear resistance, and corrosion resistance to the plating solution M, by thermally spraying the ternary intermetallic compound containing Cr, Ni, and W together with the above-described composite carbide as described above.

Here, when the total amount of the thermally-sprayed coating 12 b is assumed to be 100 mass %, the content of the composite carbide is preferably 55 to 93 mass %, and more preferably 82 to 90 mass %. The content of the ternary intermetallic compound is preferably 7 to 45 mass %, and more preferably 10 to 18 mass %.

When the content of the composite carbide is less than 55 mass % (that is, when the content of the ternary intermetallic compound exceeds 45 mass %), the contents of WC and/or Cr₂C₃ contained in the thermally-sprayed coating 12 b become short. Accordingly, there is a risk that the high temperature wear resistance of the thermally-sprayed coating 12 b may become insufficient.

When the content of the composite carbide exceeds 93 mass % (that is, when the content of the ternary intermetallic compound becomes less than 7 mass %), there is a risk that the denseness of the thermally-sprayed coating may decrease resulting in insufficient high temperature hardness. At the same time, corrosion resistance, particularly acid resistance, decreases. Here, when the denseness of the thermally-sprayed coating decreases, there are formed through pores which penetrate the thermally-sprayed coating in a coating thickness direction. The plating solution M entering from this through pores reaches the interface between the thermally-sprayed coating and the substrate. Accordingly, the thermally-sprayed coating becomes likely to be peeled from the substrate.

Also, when the total of the composite carbide is 100 mass %, the content of WC is preferably 64 to 85 mass %, and more preferably 75 to 82 mass %. When the total of the composite carbide is 100 mass %, the content of Cr₂C₃ is preferably 15 to 36 mass %, and more preferably 18 to 25 mass %. When the content of WC becomes less than 64 mass % (the content of Cr₂C₃ exceeds 36 mass %), the absolute amount of WC becomes short. Accordingly, there is a risk that the high temperature wear resistance of the thermally-sprayed coating 12 b may become insufficient. When the content of WC exceeds 85 mass % (the content of Cr₂C₃ becomes less than 15 mass %, the absolute amount of Cr₂C₃ becomes short. Accordingly, there is a risk that the thermally-sprayed coating 12 b may corrode in the plating solution M (particularly in an acidic plating solution).

Here, a thermal spraying material can be obtained as a spherical secondary particle by, for example, stirring and mixing in pure water a primary particle of the ternary intermetallic compound including Cr, Ni, and W and a primary particle of the composite carbide including WC and Cr₃C₂ to prepare a slurry, and granulating and sintering this slurry by a spray dryer method.

The ternary intermetallic compound may be a first ternary intermetallic compound having an atomic ratio of Cr:Ni:W=1.14:0.71:0.14, a second ternary intermetallic compound having an atomic ratio of Cr:Ni:W=2.5:9:1, or a third ternary intermetallic compound having an atomic ratio of Cr:Ni:W=4:15:1. Also, the ternary intermetallic compound may be a mixed ternary intermetallic compound including a mixture of these first, second, and third ternary intermetallic compounds.

The average particle size of the first particles of the ternary intermetallic compound and the composite carbide is preferably 1 to 15 μm. The average particle size of the second particles of the ternary intermetallic compound and the composite carbide is preferably 15 to 55 μm. Here, the average particle size refers to a median diameter calculated by a laser diffraction scattering measurement method.

The thermally-sprayed coating 12 b is formed by spraying the above-described thermal spraying material onto the roll body 12 a by a high velocity frame spraying method (HVOF). Thermal spraying by a high velocity frame spraying method enables the thermal spraying material to have a particle velocity of 500 m/min or more and a particle temperature of 1400° C. or higher. This allows the formation of a denser coating. In brief, since the thermal spraying material sprayed at high velocity is largely deformed to a flat shape when colliding with the roll body 12 a, the dense thermally-sprayed coating 12 b can be formed. Thus, there can be formed the thermally-sprayed coating 12 b in which the composite carbide is dispersed in the binder metal including the ternary intermetallic compound.

In the present embodiment, Cr in a state of the chemically stable ternary intermetallic compound is sprayed onto the roll body 12 a. Accordingly, oxide particles (fumes) including a Cr oxide as a main component are unlikely to be generated in the thermal spraying process. Thus, problems caused by the deposition of a Cr oxide inside and on the thermally-sprayed coating can be solved. That is, the reduction in hardness of the thermally-sprayed coating, the falling-off due to wear, the permeation of corrosive substances, and the like can be suppressed.

Hereinafter, the present invention will be more specifically described by illustrating examples.

First Example

In the first example, high temperature wear resistance, denseness, high temperature hardness, and corrosiveness were evaluated while changing the ratio between the composite carbide and the ternary intermetallic compound. The corrosiveness was evaluated on the basis of both acid resistance and alkali resistance. The ratio between WC and Cr₃C₂ constituting the composite carbide was defined to be WC:Cr₃C₂=75:25 in terms of mass %. As the ternary intermetallic compound, a mixed ternary intermetallic compound including a mixture of the first, second, and third ternary intermetallic compounds was used.

(High Temperature Wear Resistance Test)

As a tester, a friction and wear tester manufactured by Shinko Engineering Co., Ltd. was used. Three pins including SKD11 (5 mm in diameter×15 mm) as a material were pressed against a thermally-sprayed surface of a thermally-sprayed test piece with a load of 10 kg. With these pins, the test piece was subjected to sliding wear under a temperature atmosphere of 400° C. for 6 hours in an identical circular orbit. Thereafter, a cross-sectional profile image was captured at 8 locations to calculate a wear loss.

The wear loss was defined to be a volume wear loss obtained by multiplying a wear cross-sectional area by a wear track circumference. The volume wear loss of less than 3 mm³ was evaluated as “very good” indicating extremely favorable high temperature wear resistance. The volume wear loss of 3 mm³ or more and 6 mm³ or less was evaluated as “good” indicating mostly favorable high temperature wear resistance. The volume wear loss of more than 6 mm³ was evaluated as “poor” indicating unfavorable high temperature wear resistance.

(Denseness)

A thermally-sprayed coating formed on a test piece was cut, and the cross section was polished. Thereafter, the structure of the thermally-sprayed coating was observed at X400 magnification through a metallurgical microscope to check the presence or absence of pores. When pores were not clearly observed, it was evaluated as “very good” indicating extremely favorable denseness. When pores were slightly observed, it was evaluated as “good” indicating mostly favorable denseness. When pores were largely observed, it was evaluated as “poor” indicating unfavorable denseness.

(High Temperature Hardness)

As a tester, a high temperature micro hardness tester QM manufactured by Nikon Corporation was used. A diamond indenter was pressed against a test piece including a thermally-sprayed coating under a temperature atmosphere of 400° C. with a load of 300 g to measure Vickers hardness. The Vickers hardness of more than 900 HV was evaluated as “very good” indicating extremely favorable high temperature hardness. The Vickers hardness of 700 HV or more and 900 HV or less was evaluated as “good” indicating mostly favorable high temperature hardness. The Vickers hardness of less than 700 HV was evaluated as “poor” indicating unfavorable high temperature hardness.

(Acid Resistance)

A test piece including a thermally-sprayed coating was immersed in an aqueous solution of 5 vol % sulfuric acid (H₂SO₄)-0.5 vol % nitric acid (HNO₃) for 300 hours. Thereafter, acid resistance was evaluated on the basis of the damage of the thermally-sprayed coating and the elution of metal ions to the acid aqueous solution. The temperature of the aqueous solution of sulfuric acid (H₂SO₄) and nitric acid (HNO₃) was set to 40° C. under air bubbling. The elution of metal ions was judged on the basis of the change in color of the solution and the ion concentration.

When the damage (cracking, peeling) of the thermally-sprayed coating was identified, it was evaluated as “very poor” indicating extremely unfavorable acid resistance. When there was no damage of the thermally-sprayed coating and the change in color of metal ions in the solution was identified, it was evaluated as “poor” indicating unfavorable acid resistance. When there were no damage of the thermally-sprayed coating and no change in color of the solution, but the ion concentration detected by an ICP emission spectrochemical analysis was 5 ppm or more, it was evaluated as “good” indicating favorable acid resistance. When there was no damage of the thermally-sprayed coating and the ion concentration detected by an ICP emission spectrochemical analysis was not 5 ppm or more, it was evaluated as “very good” indicating extremely favorable acid resistance.

(Alkali Resistance)

A test piece including a thermally-sprayed coating was immersed in a 10 mass % aqueous solution of sodium hydroxide (NaOH) for 300 hours. Thereafter, alkali resistance was evaluated on the basis of the damage of the thermally-sprayed coating and the elution of metal ions to the aqueous solution of sodium hydroxide (NaOH). The temperature of the aqueous solution of sodium hydroxide (NaOH) was set to 40° C.

The elution of metal ions was judged on the basis of the generation state of deposits. When the damage (cracking, peeling) of the thermally-sprayed coating was identified, it was evaluated as “very poor” indicating extremely unfavorable alkali resistance. When there was no damage of the thermally-sprayed coating and deposits were identified in the solution, it was evaluated as “poor” indicating unfavorable acid resistance. When there were no damage of the thermally-sprayed coating and no identified deposits, but the ion concentration detected by an ICP emission spectrochemical analysis was 5 ppm or more, it was evaluated as “good” indicating favorable alkali resistance. When there was no damage of the thermally-sprayed coating and the ion concentration detected by an ICP emission spectrochemical analysis was not 5 ppm or more, it was evaluated as “very good” indicating extremely favorable alkali resistance. Table 1 is a table summarizing the test results for high temperature wear resistance, denseness, high temperature hardness, and corrosion resistance.

TABLE 1 TERNARY HIGH INTER- TEMPERATURE HIGH COMPOSITE METALLIC WEAR TEMPERATURE ACID ALKALI CARBIDE COMPOUND RESISTANCE DENSENESS HARDNESS RESISTANCE RESISTANCE EXAMPLE 1 51 MASS % 49 MASS % poor very good very good very good very good EXAMPLE 2 55 MASS % 45 MASS % good very good very good very good very good EXAMPLE 3 62 MASS % 38 MASS % good very good very good very good very good EXAMPLE 4 78 MASS % 22 MASS % good very good very good very good very good EXAMPLE 5 82 MASS % 18 MASS % very good very good very good very good very good EXAMPLE 6 90 MASS % 10 MASS % very good very good very good very good very good EXAMPLE 7 93 MASS %  7 MASS % very good good good good good EXAMPLE 8 96 MASS %  4 MASS % very good poor poor very poor poor

In Example 1, the content of the composite carbide was less than 55 mass %. Therefore, the high temperature wear resistance was evaluated as “poor.” In Examples 2 to 4, the content of the composite carbide was not less than 55 mass % and less than 82 mass %. Therefore, the high temperature wear resistance was evaluated as “good.” In Examples 5 to 8, the content of the composite carbide was 82 mass % or more. Therefore, the high temperature wear resistance was evaluated as “very good.” In Examples 1 to 6, the ternary intermetallic compound was contained in an amount of 10 mass % or more. Therefore, the denseness, high temperature hardness, acid resistance, and alkali resistance were evaluated as “very good”. On the other hand, in Examples 7 and 8, the content of the ternary intermetallic compound was less than 10 mass %. Therefore, the evaluations for denseness, high temperature hardness, acid resistance, and alkali resistance were lowered. In particular, the evaluation for acid resistance was drastically lowered.

Second Example

In the second example, high temperature wear resistance and corrosiveness were evaluated while changing the ratio between WC and Cr₃C₂ contained in the composite carbide. The corrosiveness was evaluated on the basis of both acid resistance and alkali resistance. As the ternary intermetallic compound, the first ternary intermetallic compound was used. The ratio between the composite carbide and the ternary intermetallic compound was the same as Example 5. The test methods were the same as those in the first example. Table 2 is a table summarizing the test results.

TABLE 2 HIGH TEMPERATURE ACID ALKALI WC Cr₃C₂ WEAR RESISTANCE RESISTANCE RESISTANCE EXAMPLE 9 61 MASS % 39 MASS % poor very good very good EXAMPLE 10 64 MASS % 36 MASS % good very good very good EXAMPLE 11 70 MASS % 30 MASS % good very good very good EXAMPLE 12 75 MASS % 25 MASS % very good very good very good EXAMPLE 13 80 MASS % 20 MASS % very good very good very good EXAMPLE 14 82 MASS % 18 MASS % very good very good very good EXAMPLE 15 85 MASS % 15 MASS % very good good very good EXAMPLE 16 90 MASS % 10 MASS % very good poor very good

In Example 9, the content of WC was less than 64 mass %. Therefore, the high temperature wear resistance was evaluated as “poor.” In Examples 10 and 11, the content of WC was not less than 64 mass % and less than 75 mass %. Therefore, the high temperature wear resistance was evaluated as “good.” In Examples 12 to 16, the content of WC was 75 mass % or more. Therefore, the high temperature wear resistance was evaluated as “very good.” In Examples 9 to 14, Cr₃C₂ was contained in an amount of more than 15 mass %. Therefore, the acid resistance and alkali resistance were both evaluated as “very good.” In Examples 15 and 16, decreasing the content of Cr₃C₂ to 15 mass % lowered the evaluation for acid resistance to “good,” and decreasing to 10 mass % lowered the evaluation for acid resistance to “poor.” However, the evaluation for alkali resistance remained “very good.” It is considered that the alkali resistance was not lowered because the ternary intermetallic compound was contained in the thermally-sprayed coating.

Comparative Example

Comparative Examples 1 to 4 illustrated in Table 3 were evaluated for high temperature wear resistance, denseness, high temperature hardness, acid resistance, and alkali resistance. The evaluation methods were the same as those in the first example and the second example.

TABLE 3 HIGH TEMPERATURE HIGH ACID ALKALI COMPOSITE BINDER WEAR TEMPERATURE RESIS- RESIS- CARBIDE METAL RESISTANCE DENSENESS HARDNESS TANCE TANCE REMARKS COMPARATIVE WC + Cr₃C₂ Cr poor poor poor poor poor WC: EXAMPLE 1 (82 MASS %) (18 MASS %) Cr₃C₂ = 4:1 COMPARATIVE WC + Cr₃C₂ Cr—Co ALLOY poor poor poor poor poor WC: EXAMPLE 2 (82 MASS %) (18 MASS %) Cr₃C₂ = 4:1 COMPARATIVE WC + Cr₃C₂ Cr—Ni ALLOY poor poor poor poor poor WC: EXAMPLE 3 (82 MASS %) (18 MASS %) Cr₃C₂ = 4:1 COMPARATIVE WC + Cr₃C₂ Ni poor poor poor very poor good WC: EXAMPLE 4 (93 MASS %) (7 MASS %) Cr₃C₂ = 73:20 For Comparative Examples 1 to 3, acid resistance and alkali resistance were evaluated as “poor.” It is considered that this is because a Cr oxide was generated in a thermal spraying heat source at high temperature. Also, for Comparative Example 4, acid resistance was evaluated as “very poor,” and alkali resistance was evaluated as “good.” It is considered that the inclusion of Ni in Comparative Example 4 inhibited corrosion under an alkali corrosive environment, but caused corrosion in the acid solution of sulfuric acid and nitric acid. For Comparative Examples 1 to 4, high temperature wear resistance, denseness, and high temperature hardness were evaluated as “poor.” It is considered that this is because a Cr oxide was generated in a thermal spraying heat source at high temperature.

REFERENCE SIGNS LIST

-   11 plating tank -   12 sink roll -   13 electrode plate -   14 conductor roll -   15 roll polisher 

1. A conductor roll for electroplating, comprising a composite carbide cermet-based thermally-sprayed coating formed on a surface of a metal roll, the composite carbide cermet-based thermally-sprayed coating including a composite carbide comprising WC and Cr₃C₂, and a ternary intermetallic compound comprising Cr, Ni, and W as a binder metal.
 2. The conductor roll for electroplating according to claim 1, wherein, when the thermally-sprayed coating is 100 mass %, the composite carbide is contained in an amount of 55 to 93 mass %, and the ternary intermetallic compound is contained in an amount of 7 to 45 mass %.
 3. The conductor roll for electroplating according to claim 1, wherein, when the composite carbide is 100 mass %, the WC is contained in an amount of 64 to 85 mass %, and the Cr₃C₂ is contained in an amount of 15 to 36 mass %. 